Deputy Commissioner Catherine Burn said that investigations into the hostage drama will take months and necessarily "have to consider the health, welfare and mental health" of those involved. As such, initial emergency medical response will give way to treatments addressing the mental health of the hostages and wider community, healthcare experts say.

NSW chief psychiatrist Dr Murray Wright, whose team administered immediate psychiatric care to escaped hostages on Monday night, said that recovery is a slow process, taking place at different rates for different people and by no means limited to those directly caught up in the drama.

"We know in times of huge tragedy, that sense of community sustains people." Photo: AP

Some level of distress or disruption to normal routines is natural and expected, rather than being an indicator of mental illness, he said, underlining the importance of support networks such as family and work.

"However, should levels of distress cause problems in day-to-day living or overwhelm a person to the point they're just not coping, or linger for a long a period," then counselling and support services are ready to help as part of a post-disaster response process.

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"You need to anticipate that healing is going to take a significant period of time. In reality, we measure recovery in months, not days or weeks," Dr Wright said.

Professor Jayashri Kulkarni from the Monash Alfred Psychiatry research centre said that responses will address the onset of acute post traumatic stress disorder (PTSD).

Its symptoms include reliving moments, flashbacks, a sense of unreality, sleeplessness and emotional numbing. Survivors guilt - questioning what might have been done to change the outcome, for example - grief and anxiety are also common.

"Each individual has their own coping style and defense mechanisms," said Prof Kulkarni. "What we hope doesn't happen is that it becomes chronic PTSD. And some people develop depression and anxiety," she said.

Therapies will be highly individualised, she said, stressing that counselling is also important for relatives, whose welfare is important for providing support to the hostage.

She added that Australian health professionals are very well versed in trauma treatment thanks to disasters such as bushfires and floods.

Dr Judy Hyde, director of the University of Sydney's department of psychology, said that on a community scale, the psychological outcomes of such a negative event can be unexpectedly positive.

Dreadful tragedies can strengthen communities and people's sense of connection, she said, suggesting that gunman Monis would not have recognised the psychological impact of his actions.

"It has the opposite effect to the intent of the perpetrator - we know in times of huge tragedy, that sense of community sustains people," she said.

The NSW Department of Health and the police are urging those who may be traumatised by the events of the past 24 hours to seek support, warning that the response may be experienced much later.

They encourage those affected to contact their local mental health service via the NSW Mental Health Line on 1800 011 511.

As part of Health Plan NSW, which was activated on Monday, a team of mental health experts was deployed in Martin Place. The small, highly experienced team provided support for and checked on the welfare of the escaped hostages. Immediate assistance focused on providing information about what mental symptoms to expect, how to manage and available support options. Prepared material was given to the individuals involved in the incident. "It's not uncommon for people to not comprehend the enormity of what they've been through," said Dr Wright. "Regardless of how they seemed at the time, we always speak to people to people a few days after the event, regardless of how they are travelling."